Manny Pacquiao of the Philippines watches as Shane Mosley goes down during their bout for the World Boxing Organization welterweight title at the Garden Arena in the MGM Grand in Las Vegas, Nevada. Pacquiao retained the crown to extend his winning streak to 14 bouts. (AFP/Gabriel Bouys)

LAS VEGAS — Manny Pacquiao toiled long and hard for his Showtime return only to find a veteran Shane Mosley on the run for most of the fight, retaining the WBO welterweight belt with a unanimous decision marked by an emphatic third round knockdown here yesterday.

Pacquiao said after the fight he was cautious in the first two rounds until he caught Mosley with a left hook that sent the aging challenger to the floor with more than a minute remaining in the third of their 12-round fight at the MGM Grand.

Many thought the fight was over right there and then.

A dazed Mosley tried to get up from the knockdown, as if he didn’t know where he was.

But he made it up despite shaky legs, survived the round, and avoided taking his first and only knockout loss in a long and cherished career.

Many thought Pacquiao didn’t actually go for the kill when Mosley looked ready to go.

Even in the succeeding rounds, the Filipino icon, who once had the penchant for knockout wins, looked like he was carrying the fight and extending the show for his fans.

Pacquiao said no, he didn’t try to carry the fight.

“If you noticed, after the fourth round, I walked back to my corner and asked my assistant to press my leg because it was tight. I had cramps on my left leg,” said the fighting congressman and the only boxer in history with eight world titles in eight weight classes.

Hours before the fight, Pacquiao figured in a vehicular accident in the vicinity of Mandalay Bay, when the SUV he was riding was struck by one of his security vehicles.

Reports said Pacquiao was shaken but unhurt after the minor incident.

“When I knocked him down, I already knew I was stronger than him. I thought I could finish him off. I wanted to fight toe to toe with him. But he ran and ran. He said in training he wanted to fight me toe to toe. That’s why I was surprised,” said Pacquiao.

From the third round, it was clear that Mosley would no longer engage.

He opted to run around, keep his distance from Pacquiao, and wait for an opening, probably one tiny mistake from the swinging Filipino champion.

But it didn’t come.

By the sixth round, some of the fans started booing.

One male fan from the upper stands could be heard shouting, “Fight! Fight!” because Mosley, who said he came to fight, started running around the ring, not taking any chances, and just fighting to survive.

In the 10th round, Pacquiao hit the canvas on a Mosley push but the referee, Kenny Bayless, ruled it a knockdown.

Pacquiao got up so quick and was terribly surprised when it was ruled a knockdown, with a minute left in the round.

It happened so fast that it looked like a knockdown, but several slow motion replays clearly showed that there was no punch landed, but a push that sent the Filipino icon down.

One judge scored that round 10-10, another in favor of Pacquiao, and the third for Mosley.

“I was surprised and I got angry,” said Pacquiao, who chased Mosley for the remainder of the round, and for the first time since the third round, he was on the attack. He added that his leg only started feeling a little better by the ninth.

Pacquiao said he never felt that those boos were directed at him.

“I think the people were booing because they wanted to see a good fight and a good exchange. But Mosley didn’t want to fight toe to toe. He was always running. What can I do? I did my best,” said Pacquiao who stretched his winning streak to 14.

Mosley came to the post-fight press conference ahead of Pacquiao.

He limped his way inside the packed media center, in gray pants and long-sleeves, with dark shades on.

He showed some swelling in his face, and the 12 rounds with Pacquiao made him look 12 years older.

He said he couldn’t fight the fight he wanted because he had blisters in the sixth round, and during the post-fight presscon he admitted that it was a slip by Pacquiao in the 10th round, and so he managed “to win some points.”

The referee approached Pacquiao’s trainer, Freddie Roach, after the fight.

“Kenny came up to me said sorry for the call and that he missed it and he apologized,” said Roach, who wasn’t too happy with the way the fight ended.

During training camp, he said it wasn’t going to be an easy fight but maintained that Pacquiao could knock Mosley out.

When the final bell sounded, Pacquiao’s face was not a face of happiness.

He shook his head a few times, and when Mosley came up to him to congratulate him, he seemed to have turned his back on the challenger who didn’t turn out as good as advertised.

Pacquiao’s assistant trainer, Buboy Fernandez, grabbed the champion by his waist and lifted him in celebration.

But he was in no mood for a victory ride.

He wasn’t happy with the victory because later on he said he also wanted to score a knockout.

Pacquiao hasn’t pulled off a stoppage for more than a year, since he stopped Miguel Cotto in the 12th and final round at the MGM in 2009.

Last year he won twice, both unanimous decisions against Joshua Clottey and Antonio Margarito.

People are starting to ask themselves. “Is age finally catching up with Pacquiao that he could no longer score knockouts?” or “Is he really too small for the welterweight class, that he can overwhelm his bigger opponents, but not finish them off?”

“I was expecting Shane to fight so we can test each other’s power. But what can I do. He kept on running. It’s not my fault,” he said.

Before he got off the ring, he faced the press box, again shaking his head, smirking and did a circling motion with his pointing finger.

“He kept on running around,” was what he meant.

“But I’m happy because I won the fight. Like what I said before, my concern is the satisfaction of the people who came to watch. I really don’t care if I hurt my face or suffer bruises as long as the people are happy.”

In the end, yes, the Pacquiao fans, part of the 16,412 that packed the Grand Garden Arena, were happy.

To say the least, most of them were happy.

But to some, the night would have been sweeter, so much sweeter, if he did knock Mosley out.

“Cramps or no cramps, he should have knocked him out,” said one, who didn’t look happy.